Surgical Monitoring System and Related Methods For Spinal Pedicle Screw Alignment

ABSTRACT

The present invention relates to a system and methods generally aimed at monitoring the angular orientation between two locations within a fluoroscopic image and especially for monitoring the angular orientation between two locations within a fluoroscopic image and a predetermined target angle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/792,377, filed Oct. 24, 2017, which is a continuation of U.S.application Ser. No. 14/841,270, filed Aug. 31, 2015, now U.S. Pat. No.9,795,451, which is a continuation of U.S. application Ser. No.12/739,950, filed Aug. 23, 2010, now U.S. Pat. No. 9,119,752, which isthe U.S. national stage of PCT/US2008/012121, filed Oct. 24, 2008, andwhich claims the benefit of priority to U.S. provisional apps.61/000,349 filed Oct. 24, 2007, and 61/196,266, filed Oct. 15, 2008, theentire contents each of which are expressly incorporated by referenceinto this disclosure as if they were set forth in their entiretiesherein.

BACKGROUND OF THE INVENTION I. Field of the Invention

The present invention relates generally to determining a desiredtrajectory and/or monitoring the trajectory of surgical instruments andimplants and, more particularly, doing so during spinal surgery,including but not limited to ensuring proper placement of pedicle screwsduring pedicle fixation procedures and ensuring proper trajectory duringthe establishment of an operative corridor to a spinal target site.

II. Discussion of the Art

Determining the optimal or desired trajectory for surgical instrumentsand/or implants and monitoring the trajectory of surgical instrumentsand/or implants during surgery have presented challenges to surgeonssince the inception of surgery itself. One example is pedicle fixation,which is frequently performed during spinal fusions and other proceduresdesigned to stabilize or support one or more spine segments. Pediclefixation entails securing bone anchors (e.g. pedicle screws) through thepedicles and into the vertebral bodies of the vertebrae to be fixed orstabilized. Rods or other connectors are used to link adjacent pediclescrews and thus fix or stabilize the vertebrae relative to each other. Amajor challenge facing the surgeon during pedicle fixation is implantingthe pedicle screws without breaching, cracking, or otherwisecompromising the pedicle wall, which may easily occur if the screw isnot properly aligned with the pedicle axis. If the pedicle (or morespecifically, the cortex of the medial wall, lateral wall, superior walland/or inferior wall) is breached, cracked, or otherwise compromised,the patient may experience pain and/or neurologic deficit due tounwanted contact between the pedicle screw and delicate neuralstructures, such as the spinal cord or exiting nerve roots, which lie inclose proximity to the pedicle. A misplaced pedicle screw oftennecessitates revision surgery, which is disadvantageously painful forthe patient and costly, both in terms of recovery time andhospitalization.

The present invention is aimed primarily at eliminating or at leastreducing the challenge associated with determining the optimal ordesired trajectory for surgical instruments and/or implants andmonitoring the trajectory of surgical instruments and/or implants duringsurgery.

SUMMARY OF THE INVENTION

The present invention facilitates the safe and reproducible use ofsurgical instruments and/or implants by providing the ability todetermine the optimal or desired trajectory for surgical instrumentsand/or implants and monitor the trajectory of surgical instrumentsand/or implants during surgery. By way of example only, the presentinvention may be used to ensure safe and reproducible pedicle screwplacement by monitoring the axial trajectory of surgical instrumentsused during pilot hole formation and/or screw insertion.Neurophysiologic monitoring may also be carried out during pilot holeformation and/or screw insertion. It is expressly noted that in additionto its uses in pedicle screw placement, the present invention issuitable for use in any number of additional surgical procedures wherethe angular orientation or trajectory of instrumentation and/or implantsand/or instrumentation is important, including but not limited togeneral (non-spine) orthopedics and non-pedicular based spineprocedures. It will be appreciated then that while the surgicalinstruments are generally described below as pedicle access tools,cannulas, retractor assemblies, and imaging systems (e.g. C-arms),various other surgical instruments (e.g. drills, screw drivers, taps,etc.) may be substituted depending on the surgical procedure beingperformed and/or the needs of the surgeon.

A surgical trajectory system may include an angle-measuring device(hereafter “tilt sensor”) and a feedback device. The tilt sensormeasures its angular orientation with respect to a reference axis (suchas, for example, “vertical” or “gravity”) and the feedback device maydisplay or otherwise communicate the measurements. Because the tiltsensor is attached to a surgical instrument the angular orientation ofthe instrument, may be determined as well, enabling the surgeon toposition and maintain the instrument along a desired trajectory duringuse.

The tilt sensor may include a sensor package enclosed within a housing.The housing is coupled to or formed as part of a universal clip toattach the tilt sensor to a surgical instrument. The sensor package maycomprise a 2-axis accelerometer which measures its angular orientationin each of a sagittal and transverse plane with respect to the actingdirection of gravity. The sagittal orientation corresponds to acranial-caudal angle and the transverse orientation corresponds to amedial-lateral angle. The sensor package is preferably situated suchthat when the tilt sensor is perpendicular to the direction of gravity,the inclinometer registers a zero angle in both the sagittal andtransverse planes. Thus, when the tilt sensor is fixed perpendicularlyto the longitudinal axis of the surgical instrument, the angularorientation of the longitudinal axis of the instrument is determinedrelative to gravity. Alternatively, a 3-axis sensor may be used. The3-axis sensor may comprise a 2-axis accelerometer to measure sagittaland transverse orientation and either a gyroscope and/or one or moremagnetometers (e.g. a single 3-axis magnetometer or a combination of a1-axis magnetometer and a 2-axis magnetometer) to measure thelongitudinal axial rotation of the instrument.

A surgical instrument for use with the surgical trajectory system maycomprise, by way of example only, a pedicle access probe. The instrumentmay generally comprise a probe member having a longitudinal axis and ahandle. The probe member may be embodied in any variety ofconfigurations that can be inserted through an operating corridor to apedicle target site and bore, pierce, or otherwise dislodge and/orimpact bone to form a pilot hole for pedicle screw placement. The probemember may be composed of any material suitable for surgical use andstrong enough to impact bone to form a pilot hole. In one embodiment,the material may be capable of conducting an electric current signal toallow for the use of neurophysiologic monitoring.

The handle may be permanently or removably attached to the probe memberand may be shaped and dimensioned in any of a number of suitablevariations to assist in manipulating the probe member. In someembodiments, the handle includes a cutout region for accommodatingattachment of the universal clip. In other embodiments, the handleincludes an integral cavity for receiving the tilt sensor directly. Instill other embodiments the tilt sensor is permanently integrated intothe instrument handle.

A control unit may be communicatively linked to the tilt sensor via ahard wire or wireless technology. The feedback device may communicateany of numerical, graphical, and audio feedback corresponding to theorientation of the tilt sensor in the sagittal plane (cranial-caudalangle) and in the transverse plane (medial-lateral angle).

In general, to orient and maintain the surgical instrument along adesired trajectory during pilot hole formation, the surgical instrumentis advanced to the pedicle (through any of open, mini-open, orpercutaneous access) while oriented in the zero-angle position. Theinstrument is then angulated in the sagittal plane until the propercranial-caudal angle is reached. Maintaining the proper cranial-caudalangle, the surgical instrument may then be angulated in the transverseplane until the proper medial-lateral angle is attained. Once thecontrol unit or secondary feedback device indicates that both themedial-lateral and cranial caudal angles are matched correctly, theinstrument may be advanced into the pedicle to form the pilot hole,monitoring the angular trajectory of the instrument until the holeformation is complete.

Before the pilot hole is formed, the desired angular trajectory (e.g.the cranial-caudal angle and the medial-lateral angle) must first bedetermined. Preoperative superior view MRI or CAT scan images are usedto determine the medial-lateral angle. A reference line is drawn throughthe center of the vertebral body and a trajectory line is then drawnfrom a central position in the pedicle to an anterior point of thevertebral body. The resulting angle between the trajectory line and thereference line is the desired medial-lateral angle to be used in formingthe pilot hole.

The cranial-caudal angle may be determined using an intraoperativelateral fluoroscopy image incorporating a vertical reference line.Again, a trajectory line is drawn from the pedicle nucleus to ananterior point of the vertebral body. The resulting angle between thetrajectory line and the vertical reference line is the desiredcranial-caudal angle to be used in forming the pilot hole. A protractoroutfitted with a tilt sensor may be provided to assist in determiningthe cranial-caudal angle in the operating room. Alternatively, thecranial-caudal angle may be calculated preoperatively using imagingtechniques that provide a lateral view of the spine. The medial-lateraland cranial-caudal angles should be determined for each pedicle that isto receive a pedicle screw. Alternate and/or additional methods forpredetermining the pedicle angles are also contemplated and may be usedwithout deviating from the scope of the present invention.

According to one embodiment of the present invention, a reticle may beprovided to attach the tilt sensor to a standard C-arm. The reticlecomprises an integrated sensor and a mount which may attach to theC-arm. The reticle further comprises an adjustable laser. The laser maybe aimed along the C-arm axis. In use the laser cross-hair will mark atarget incision site on a patient when the C-arm is oriented in linewith the pedicle axis. Radiopaque markers are also integrated into thereticle. The markers provide a reference for properly aligning thefluoroscopic images.

To select a starting point for pedicle penetration, the C-arm may beplaced in the trajectory lateral position. From the trajectory lateralposition the C-arm may be rotated back to the A/P position whilemaintaining the radial rotation imparted to achieve the trajectorylateral position. A surgical instrument may be advanced to the targetsite and positioned on the lateral margin of the pedicle, the preferredstarting point according to this example. The depth of penetration ofthe surgical instrument may be checked during advancement by rotatingthe C-arm back to a trajectory lateral view.

Alternatively, the starting point may be determined using an “owls eye”view. The C-arm may be oriented such that it is aligned with both themedial-lateral and cranial-caudal angles as discussed above. The tip ofthe pedicle access instrument is placed on the skin so that the tip islocated in the center of the pedicle of interest on the fluoroscopicimage; and thereafter the instrument is advanced to the pedicle. Anotherfluoroscopic image is taken to verify that the tip of the instrument isstill aligned in the center of the pedicle.

Using the “owls eye” view, a standard surgical instrument may be guidedalong a pedicle axis without the use of an additional tilt sensor on thesurgical instrument. In the “owls eye” image, a surgical instrumentproperly aligned with the pedicle axis will appear as a black dot. Oncealigned, the surgical instrument may be advanced through the pediclewhile ensuring that it continues to appear as only a dot on thefluoroscopy image. The depth of penetration may again be checked with atrajectory lateral image.

Neurophysiologic monitoring may be carried out in conjunction with thetrajectory monitoring performed by the surgical trajectory system. Thesurgical trajectory system may be used in combination withneurophysiologic monitoring systems to conduct pedicle integrityassessments before, during, and after pilot hole formation, as well asto detect the proximity of nerves while advancing and withdrawing thesurgical instrument from the pedicle target site. By way of exampleonly, a neurophysiology system is described which may be used inconjunction with the surgical trajectory system. By way of furtherexample, the neurophysiology system and the surgical trajectory systemmay be integrated into a single system. Neurophysiology monitoring andtrajectory monitoring may be carried out concurrently and the controlunit may display results for each of the trajectory monitoring functionand any of a variety of neurophysiology monitoring functions, including,but not necessarily limited to, Twitch Test, Free-run EMG, Basic ScrewTest, Difference Screw Test, Dynamic Screw Test, Nerve Detection, NerveHealth, MEP, and SSEP.

The neurophysiology system includes a display, a control unit, a patientmodule, one or more of an EMG harness and an SSEP harness, a host ofsurgical accessories (including an electric coupling device) capable ofbeing coupled to the patient module via one or more accessory cables.According to one embodiment, the electric coupling device may be thetilt sensor clip.

To perform the neurophysiologic monitoring, the surgical instrument isconfigured to transmit a stimulation signal from the neurophysiologysystem to the target body tissue (e.g. the pedicle). As previouslymentioned, the surgical instrument probe members may be formed ofmaterial capable of conducting the electric signal. To prevent shuntingof the stimulation signal, the probe members may be insulated, with anelectrode region near the distal end of the probe member for deliveringthe electric signal and a coupling region near the proximal end of theprobe member for coupling to the neurophysiology system.

According to one exemplary method of using the systems and methodsdescribed herein, a pedicle screw may be implanted in a target pedicleaccording to the following steps. First, preoperative measurementscorresponding to the medial/lateral angle of the pedicle are determinedusing suitable imaging technology, such as for example, MRI. Level theC-arm and then attach the laser reticle to the C-arm using theintegrated tilt sensor and LED indicators to align the laser reticleinto proper position and the adjustable clamps to lock the reticle inplace. Adjust the laser cross-hairs if necessary such that the center ofthe cross-hairs align with the calibrated center of the C-arm emitter.Select from the navigated guidance system whether fluoroscopy will beused and indicate which side of the body the C-arm is positioned. Ensurethe patient is still aligned properly on the table and then measure thecranial/caudal angles. Use the virtual protractor to determine thecranial/caudal angles and then enter the predetermined medial/lateralangles into the system. Return the C-arm to the A/P position to verifyagain that the patient hasn't moved. Orient the C-arm into owls eyeposition. Mark the skin where laser cross-hairs direct and then repeatthe steps for each pedicle to be instrumented. Make a hole with apedicle access probe and advance the probe to the spine. Ensure that thepedicle probe is docked on a good starting point with the C-arm and thenadvance the probe into the pedicle, repeating again for each pedicle tobe instrumented.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is an exemplary view of a surgical trajectory system, including asensor clip, C-arm, laser reticle, surgical instrument and control unit,according to one embodiment of the present invention;

FIG. 2 is a perspective view of a tilt sensor clip of the surgicaltrajectory system of FIG. 1, according to one embodiment of the presentinvention;

FIG. 3 is a perspective view of a tilt sensor, the outer housing shownin dashed lines to make visible the sensor situated within the housing,according to one embodiment of the present invention;

FIG. 4 is a perspective view depicting the bottom of the tilt sensor,according to one embodiment of the present invention;

FIG. 5 is a close up view of a handle portion of a surgical instrument,according to one embodiment of the present invention;

FIG. 6 and FIG. 7 illustrate a sensor clip connector used to attach thetilt sensor to a surgical instrument, according to one embodiment of thepresent invention;

FIG. 8 is an illustration of an operating theater equipped with asurgical table, C-arm fluoroscope, fluoroscope monitor, practitioner,and patient;

FIG. 9 is a front view of the C-arm of FIG. 8 oriented in an A/Pposition for generating an A/P fluoroscopic image;

FIG. 10 is front view of the C-arm of FIG. 8 oriented in a lateralposition for generating a lateral fluoroscopic image;

FIG. 11A and FIG. 1B are front views of the C-arm of FIG. 8 orientedaccording to desired medial-lateral angles between the A/P position ofFIG. 9 and the lateral position of FIG. 10;

FIG. 12A and FIG. 12B are side views of the C-arm of FIG. 8 orientedaccording to various cranial-caudal angles;

FIG. 13-FIG. 19 are exemplary views of a laser reticle equipped with anintegrated tilt sensor, radiopaque cross-hairs, and laser light,according to one embodiment of the present invention;

FIG. 20 is a top view of a vertebral body showing the medial-lateralangle A1 of the pedicle axis;

FIG. 21 is a side view of a vertebral body showing the cranial-caudalangle A2 of the pedicle axis;

FIG. 22 illustrates a superior view preoperative MRI image used todetermine the proper medial-lateral angle for hole formation, accordingto one embodiment of the present invention;

FIG. 23 illustrates an intraoperative lateral fluoroscopy image used todetermine the proper cranial-caudal angle for hole formation, accordingto one embodiment of the present invention;

FIG. 24 is an exemplary screen display of the surgical trajectory system10 incorporating both alpha-numeric and graphical indicia, according toone embodiment of the present invention;

FIG. 25 is an exemplary screen display of the surgical trajectory system10 incorporating both alpha-numeric and graphical indicia, according toanother embodiment of the present invention;

FIG. 26-FIG. 36 are exemplary screen displays of the surgical trajectorysystem 10 incorporating alpha-numeric, graphical indicia, andfluoroscopic image data, and various control features according toanother embodiment of the present invention;

FIG. 37-FIG. 46 are exemplary screen displays of the surgical trajectorysystem 10 incorporating alpha-numeric, graphical indicia, andfluoroscopic image data, and various control features according to yetanother embodiment of the present invention; and

FIG. 47 is a perspective view of an exemplary neuromonitoring system foruse in conjunction with the surgical trajectory system of FIG. 1,according to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The systems disclosed herein boast a variety ofinventive features and components that warrant patent protection, bothindividually and in combination.

Various embodiments are described of a trajectory monitoring system andsurgical uses thereof for enhancing the safety and efficiency ofsurgical procedures. In one example, set forth by way of example only,the present invention may facilitate safe and reproducible pedicle screwplacement by monitoring the axial trajectory of various surgicalinstruments used during pilot hole formation and/or screw insertion. Inanother example, set forth by way of example only, intraoperativeimaging performance may be improved and radiation exposure minimized bymonitoring the precise orientation of the imaging device. In yet anotherexample, monitoring the orientation of surgical access instruments canaid in both the insertion and positioning of the access instrumentsthemselves, as well as, aiding in the later insertion of instrumentsand/or implants through the surgical access instruments. While the aboveexamples are described in more detail below, it is expressly noted thatthey are set forth by way of example and that the present invention maybe suitable for use in any number of additional surgical actions wherethe angular orientation or trajectory of instrumentation and/or implantsis important. By way of example only, the present invention may beuseful in directing, among other things, the formation of tunnels forligament or tendon repair and the placement of facet screws.Accordingly, it will be appreciated then that while the surgicaltrajectory system is generally discussed herein as being attached toinstruments such as pedicle access tools, C-arms, dilating cannulas, andtissue retractors, other instruments (e.g. drills, screw drivers, taps,inserters, etc.) may be substituted depending on the surgical procedurebeing performed and/or the needs of the surgeon. In a further aspect ofthe present invention, the trajectory monitoring system may be used inconjunction with, or integrated into, a neurophysiology system forassessing one or more of pedicle integrity and nerve proximity, amongothers functions, as will be described below.

Details of the surgical trajectory system are discussed in conjunctionwith a first exemplary use thereof for monitoring pilot hole formation(and/or screw insertion) during pedicle screw placement. As used herein,pilot hole formation is meant to encompass any of, or any combinationof, creating a hole in bone (such as, for example only, by awling,boring, drilling, etc.) and preparing a previously formed hole (such as,for example only, by tapping the hole).

With reference now to FIG. 1, there is shown, by way of example only,one embodiment of a surgical trajectory system 10 including a tiltsensor clip 12 (also referred to as “tilt sensor”) engaged with asurgical instrument 14, a feedback and control device comprising acontrol unit 16, and a laser reticle 18 coupled to a C-arm 20. The tiltsensor clip 12 measures its own angular orientation with respect to areference axis, such as vertical or gravity. The control unit 16provides feedback related to the angle measurements obtained by the tiltsensor clip 12 for reference by a practitioner and receives user input.The tilt sensor clip 12 attaches to surgical instrument 14 in a knownpositional relationship such that the angular orientation of theinstrument 14 may be determined with respect to the same reference axis.This enables the surgeon to position and maintain the instrument 14along a desired trajectory path during use. For example, during pilothole formation, surgical instrument 14 may be aligned and advanced alonga pre-determined pedicle axis, thereby decreasing the risk of breachingthe pedicle wall.

Tilt sensor 12, illustrated in FIGS. 2-4, includes a sensor package 22(FIG. 3) enclosed within a housing 24. The housing 24 may be made from asurgical grade plastic, metal, or any material suitable for use in thesurgical field. Housing 24 is configured to snugly couple with thesurgical instrument 14 in a known positional relationship, as will bedescribed below.

In one embodiment, sensor package 22 comprises a 2-axis accelerometerthat measures angular orientation with respect to the acting directionof gravity. The angular orientation of tilt sensor 12 is measured in asagittal plane and a transverse plane. By way of example, theorientation of the tilt sensor 12 in the transverse plane represents amedial-lateral angle A1(i) with respect to a patient and the directionof gravity. Orientation in the sagittal plane represents acranial-caudal angle A2(i) with respect to the direction of gravity andthe patient. Sensor package 22 is preferably situated within housing 24such that when housing 24 is perpendicular to the direction of gravity,the accelerometer registers zero angle in both the sagittal andtransverse planes (i.e. the zero-angle position or A1(i)=0 and A2(i)=0).In other words, both the cranial-caudal angle and medial-lateral angleare equal to zero. Thus, when tilt sensor 12 is fixed perpendicular tothe longitudinal axis of the surgical instrument 14, the angularorientation of the instruments longitudinal axis may be determinedrelative to gravity.

Utilizing only a 2-axis accelerometer, the accuracy of the tilt sensor12 may be affected by movement around the third, rotational axis. Tocounter this, measurements should preferably be taken only when at leastone of the longitudinal axis 26 and transverse axis 28 tilt sensor 12are aligned with a selected reference frame, such as for example, thelongitudinal axis of the patient's spine (i.e. the tilt sensor 12 shouldbe in approximately the same rotational alignment for each measurement).In one embodiment, this may be accomplished effectively using visualaids to help keep the tilt sensor 12 in line with the reference frameand/or ensure measurements may be taken when the tilt sensor 12 appearsto be in this correct rotational position. By way of example only, thesensor clip 12 attaches to the instrument 14 such that a free end of theclip may “point” to the patients feet when the sensor 12 is in thecorrect-rotational position. In the event the surgical instrument 14 isinadvertently or purposely rotated during use, the practitioner needonly continue, or reverse rotation until the tilt sensor 12 againappears to be perpendicular to the long axis of the spine. Alternatively(or in addition to), various markings or other indicia (not shown) maybe included on one or more of the tilt sensor 12 and the surgicalinstrument 14 to ensure proper alignment prior to obtainingmeasurements.

In an alternative embodiment, the sensor package 22 may be configuredsuch that it may account for, or at least measure, rotation (e.g. a“3-axis sensor”). In one embodiment, the sensor package 22 includes a2-axis accelerometer augmented by a gyroscope (not shown), which maycomprise any number of commercially available gyroscopes. While theaccelerometer again measures the angular orientation of the tilt sensor12 with respect to gravity, the gyroscope detects movement about therotational or z-axis. By monitoring the rate of rotation and time, thesystem may determine the degrees of rotation imparted on the surgicalinstrument 14 (and tilt sensor 12). The control unit 16 may indicate tothe user that the sensor 12 is not aligned in the correct referenceframe such that the user may take steps to correct the alignment priorto taking measurements. The control unit 16 may display feedbackaccording to any number of suitable methods. By way of example, thefeedback may utilize numeric indicia to indicate the degree ofmisalignment, color indicia, such as red or green indicating therotational status (e.g. aligned or misaligned), audible alert tones(e.g. low frequency tones for non-alignment and high frequency tones forproper alignment or visa versa or any combination thereof), etc.Alternatively, the system may be configured to correct the angle dataoutput based on the degree of rotation detected. In this manner, angledata from the tilt sensor 12 may be acquired from any rotationalposition. A button (not shown) may be provided on the tilt sensor 12and/or control unit 16 to initially zero the sensor package 22 when itis aligned with the reference frame.

In another embodiment, the sensor package 22 accounts for rotationalmovement by utilizing magnetometers (not shown) in conjunction with the2-axis accelerometers, where the magnetometer may comprise any number ofcommercially available magnetometers. The sensor package 22 includes atriplet of magnetic sensors oriented perpendicular to each other, onepointing in the x-axis, one in the y-axis, and third pointing in thez-axis. The magnetic sensors in the x and y axis act as a compass andcalculate a heading of tilt sensor 12 relative to magnetic north. Thethird magnetometer in the z-axis and the x and y axis accelerometersmonitor the tilt permitting the “compass” to work when it is not levelto the ground. Since the sensor package 22 monitors for angularorientation in the x-axis and y-axis and maintains a constant headingreference, the system 10 may calculate the amount of axial rotationrelative to an established reference frame (i.e. the patient). Thecontrol unit 16 may again be configured to indicate the rotationalstatus of the tilt sensor 12 to the user, allowing them to realign thesensor 22 with the proper reference frame prior to establishing areading. The feedback device 16 may again utilize numeric indicia toindicate the degree of misalignment, color indicia, such as red or greenindicating the rotational status (e.g. aligned or misaligned), audiblealert tones (e.g. low frequency and/or volume tones for non-alignmentand high frequency and/or volume tones for proper alignment or visaversa or any combination thereof), etc.

A surgical instrument 14, according to one embodiment, is illustrated inFIG. 4. Surgical instrument 14 may comprise a pedicle access probe. Byway of example only, instrument 14 may be any of the insulated pedicleaccess probes described in detail in the commonly owned and co-pendingU.S. patent application Ser. No. 11/448,237, entitled “Insulated PedicleAccess System and Related Methods,” and filed on Jun. 6, 2006, theentire contents of which is incorporated by reference as if set forthherein in its entirety. Instrument 14 comprises generally a probe member30, having a longitudinal axis 32, and a handle 34. Probe member 30 maybe embodied in any variety of configurations that can be insertedthrough an operating corridor to a pedicle target site and bore, pierce,or otherwise dislodge and/or impact bone to form a pilot hole forpedicle screw placement. Probe member 30 may be generally cylindrical inshape, however, probe member 30 may be provided in any suitable shapehaving any suitable cross-section (e.g. generally oval, polygonal,etc.). A distal region 36 of probe member 30 may have a shaped tip 38formed of any number of shapes generally suited to effect pilot holeformation, such as, by way of example only, a beveled point, doublediamond, drill bit, tap, and a generally tapered awl. A proximal region40 of probe member 30, accessible via a cutout 42 in the handle 34, maybe configured to couple the housing 24 of sensor clip 12. Probe member30 may be composed of any material suitable for surgical use and strongenough to impact bone to form a pilot hole. In one embodiment, thematerial may also be capable of conducting an electric current signal toallow for the use of neurophysiologic monitoring. By way of exampleonly, probe member 30 may be composed of titanium, stainless steel, orother surgical grade alloy. The distal region 36 may also be equippedwith a retractable insulation sheath 44. The sheath 44 ensures maximumefficiency of an electrical stimulation signal that may be delivered tothe shaped tip 38 during neurophysiologic monitoring that may beconducted in conjunction with the surgical trajectory monitoring ofsystem 10, as described below.

Handle 34 may be permanently or removably attached to probe member 30along the proximal region 40. Handle 34 may be shaped and dimensioned inany of a number of suitable variations to assist in manipulating probemember 30. By way of example only, the handle 34 may be generallyT-shaped such as the handle pictured in FIG. 4. Other suitable shapesfor handle 34 may include, but are not necessarily limited to, generallyspherical, ellipsoidal, and egg-shaped. Sensor clip 12 forms a sturdyconnection with probe member 30 such that the tilt sensor 12 ismaintained in a position perpendicular to the longitudinal axis 32 ofprobe member 30. When the longitudinal axis 32 of probe member 30 isparallel to the direction of gravity, the tilt sensor 12 isperpendicular to the direction of gravity (i.e. the zero-angleposition). In other words, when the longitudinal axis 32 of probe member30 is parallel to the acting direction of gravity, both thecranial-caudal angle and the medial-lateral angle will be zero-degrees.

With reference to FIGS. 2-7, sensor clip 12 will be further described.To secure the sensor clip 12 to surgical instrument 14, housing 24includes a fastener end 46 dimensioned to snugly receive at least aportion of instrument 14. By way of example only, fastener end 46comprises an end hook 48, and a handle receiver 50. To maintain a snugfit with the instrument 14, the end hook 48 is configured to snap on andtightly grasp the proximal region 40, as illustrated in FIG. 4. Toattach the clip 12 to instrument 14, the end hook 48 is fitted onto theproximal end 40 of the instrument 14. Thereafter the housing 24 isrotated until the handle receiver 50 fully engages with the handle 34 ofthe instrument 14 (FIGS. 6-7). FIG. 6 illustrates, by way of exampleonly, a the proximal end 40 (shown in cross-section) tightly positionedwithin the end hook 48 and before engaging the handle 34 (also shown incross-section) in the handle receiver 50. FIG. 7 illustrates the handle34 (again in cross-section) after the clip 12 has been rotated intoposition with the handle 34 fully engaged in the handle receiver 50.Once fully engaged, fastener end 46 is dimensioned to prevent theunintentional disengagement of instrument 14 from the sensor clip 12.When engaged, sensor clip 12 extends perpendicular to the longitudinalaxis 32 of instrument 14. To release the surgical instrument 14, theclip 12 may be rotated to disengage the handle receiver 50 from thehandle 34, and the end hook 48 may be released.

Also illustrated in FIGS. 2-4 and 6-7 is a secondary feedback system 52,integrated into the sensor clip 12. By way of example only, secondaryfeedback system 52 comprises a collection of LED light indicators toprovide an indication of the angular orientation of surgical instrument14 relative to a reference orientation. The collection of LED's includesfour LED directional lights 54-60, a central LED light 62, and afunction LED light 64. The four LED directional lights 54-60 areindependently operated to provide an indication to the user of thesensors 12 (and hence, the instrument 14) angular position relative to adesired position (as determined, for example, by predetermined anglemeasurements captured by or inputted into the system 10). By way ofexample only, two opposing LED lights 54 and 56 may correspond to theorientation of the sensor 12 in the cranial-caudal direction and theother two opposing LED lights 58 and 60 may correspond to theorientation in the medial-lateral directions. According to one example,the LED directional lights 54-60 will light to indicate the direction inwhich the instrument 14 needs to be adjusted to align with the desiredtrajectory. Thus, (by way of example) if the instrument is properlyaligned in the medial-lateral direction but not in the cranial-caudaldirection then one if lights 54 and 56 will light up to indicate thatthe instrument needs to be moved in the direction of the lighted LED(either 54 or 56 depending upon whether the instrument needs to beadjusted in the cranial direction or the caudal direction), if however,the instrument 14 is not aligned in either the cranial-caudal directionor the medial-lateral direction, one each of LEDS 54-56 and 58-60 willlight to indicate which direction (i.e. either cranial or caudal andeither left or right, respectively) that the instrument 14 needs to beadjusted to align with the desired trajectory.

The control unit 16 is communicatively linked to tilt sensor clip 12 andfunctions to provide feedback to the surgeon regarding the angle of thetilt sensor 12 and instrument 14 relative to the desired angles (e.g.predetermined medial-lateral and cranial-caudal angles) as well asreceive user input related to various aspects of the trajectory system10. Byway of example only, the control unit 16 includes a display 66which may show one or more or alpha-numeric, graphic, and color indiciaindicative of the sensor 12 trajectory, imported fluoroscopic or otherimages, patient and or user information, and other system relatedinformation. The control unit 16 may also receive user input, such as byway of example, user selectable parameters and/or preferences, procedurerelated data (including but not necessarily limited to predeterminedmedial-lateral angles, predetermined cranial-caudal angles), etc. By wayof further example, the control unit 16 display 66 may include toolswhich may be utilized by the user, such as by way of example only, avirtual protractor for predetermining angles. Various features andaspects of the control unit 16 and display 66 functionality arediscussed in more detail below. In addition to display 66, the controlunit 16 may be configured to utilize audio indicators as well. By way ofexample, the control unit 16 may utilize a code based on the emission ofaudio tones to indicate the angular orientation of the tilt sensor 12relative to predetermined reference angles corresponding to the desiredtrajectory. One method for implementing an audio code involves varyingone or more of the volume, pitch, frequency, pulse rate, and length ofthe audio tone based on the determined orientation of the sensor 12relative to the predetermined orientation ranges. Audio feedback may beused alone, or in combination with one or both of the alpha-numeric,graphic, and color indicia previously described. In one embodiment, afirst audible signal may be indicative of an optimal variance betweenthe trajectory of the instrument and at least one of the first andsecond determined angular relationships between the sensor 12 and thereference direction. A second audible signal may be indicative of anunacceptable variance between the trajectory of the instrument and atleast one of the first and second determined angular relationshipsbetween the sensor 12 and the reference direction. A third audiblesignal may be indicative of an acceptable yet not optimal variancebetween the trajectory of the instrument and at least one of the firstand second determined angular relationships between the sensor 12 andthe reference direction.

The communication link between the sensor clip 12 and may beaccomplished via hard-wire (e.g. data cable 68 of FIG. 1) and/or viawireless technology, in which case the tilt sensor 12 and control unit16 may include additional hardware commonly used for enabling suchwireless communication. If communicatively linked to the feedback device16 via hard-wire, the position of the feedback device 16 should be suchthat the tilt sensor 12 may move freely without tensioning the datacable 68.

According to another aspect of the present invention, the laser reticle18 is attached to C-arm 20 (fluoroscope) to aid in orienting the C-arm20 into an advantageous position. By way of example only, it may beadvantageous during pedicle screw placement to orient the C-arm 20 in anowl's eye or oblique position (i.e. the trajectory of the x-ray beam isdirectly in line with the angular trajectory of the pedicle). Thereticle 18 is equipped with an integrated sensor package 70. Sensorpackage 70 comprises an accelerometer similar to the sensor package 22of clip 12 (such that a repeat discussion is not necessary). Including atilt sensor package 70 in the reticle allows the system 10 to determinethe angular position of the reticle 18, and hence the C-arm 20 to whichit is attached, with respect to gravity. The C-arm 20 and laser reticle18 will now be discussed in more detail.

With reference to FIG. 8 there is shown a typical operating theatre inwhich a practitioner 72 may perform surgical procedures on a patient 74.The patient 74 is positioned on a radiolucent operating table 76.Arrayed around the table 76 are a standard C-arm 20, comprising a frame78, a signal transmitter 80, and a signal receiver/image intensifier 82,and the control unit 16 which receives and displays video feed from theC-arm 20, allowing live fluoroscopic images to be integrated with thetrajectory monitoring system 10. In use, an x-ray beam 84, having acentral axis 86, may be directed from the signal transmitter 80 througha desired area of patient 74 and picked up by the signal receiver 82. Animage of the patient's 74 body tissue located in the path of beam 84 maybe generated and displayed on the display 66. It should be appreciatedthat while the C-arm 20 is discussed herein generally for use duringspine surgery to capture images of the spine, such discussion is forexemplary purposes only. It will be understood that the C-arm 20 andlaser reticle 18 combination may be utilized for imaging in a widevariety of surgical procedures.

As illustrated in FIGS. 9-12, the C-arm frame 78 may be adjusted toalter the path of the beam 84, and thus the image that is generated. InFIG. 9 the frame 78 is oriented such that beam 84 travels parallel tothe direction of gravity. With the patient in the prone position, asshown herein, this position of frame 78 generates an anterior-posterior(A/P) image. This position of C-arm 20 is referred to hereafter as theA/P position. Rotating the frame 90° in a medial-lateral direction(through a transverse plane), as depicted in FIG. 10, directs the beam84 perpendicular to the direction of gravity and generates a lateralimage. This position of the C-arm 20 is referred to as the lateralposition. A/P and lateral images may both be useful during a spinalprocedure and the C-arm may be adjusted between the A/P and lateralpositions numerous times during the procedure. As illustrated in FIGS.11A-11B, the frame 78 may also be oriented in any position within thetransverse plane between the A/P and lateral positions, such that thebeam 84 forms an angle A1(c) (the medial-lateral angle) between zero and90° with respect the direction of gravity. Furthermore, as illustratedin FIGS. 12A-12B, the frame 78 may also be rotated in a cranial-caudaldirection (within a sagittal plane) such that the beam 84 forms anotherangle A2(c) (the cranial-caudal angle) with respect to the direction ofgravity. By way of example only, the C-arm 20 may be oriented such thatone or both of angles A1(c) and A2(c) correspond to the desired axis oftrajectory of a pedicle bone, i.e. angles A1 and A2 (owl's eye oroblique view), as will be discussed in more detail below.

By attaching the reticle 18 with integrated tilt sensor package 70 tothe C-arm20 in a known positional relationship, the angular orientationof the C-arm with respect to the reference axis (gravity) may bedetermined. This enables the practitioner to quickly position the C-arm20 in a known orientation, such as, by way of example only, the preciseorientation in which a previous image was acquired. Doing so mayeliminate the time and extra radiation exposure which is often enduredwhile acquiring numerous images while “hunting” for the right image.Attaching the sensor 70 (via reticle 18) to the C-arm may further enablethe practitioner to determine the angular orientation of anatomicalstructures within the patient (e.g. vertebral pedicles), as will bedescribed below. This may be advantageous, for example only, when thepractitioner is performing pedicle fixation and preoperative images(such as the MRI or CAT images which may be used to determine thepedicle axis angle A1) are not available for preoperative planning, asdescribed above.

According to one embodiment laser reticle 18 may be attached to thereceiver. 82 of the C-arm 20, as pictured in FIG. 1. FIG. 13 illustratesone embodiment of laser reticle 18 comprising a reticle frame 1152,radiopaque cross hair marker 1154, radiolucent front cover 1158,radiolucent back plate 1159, adjustable clamps 1160, sensor tilt LEDindicators 1164, and an adjustable laser emitter system 96. FIG. 14illustrates an exploded view of laser reticle 18. The reticle 18 isconfigured to generate a reference cross-hair viewable in fluoroscopicimages generated by C-arm 20. Other benefits may also be gained by usinglaser reticle 18, such as the benefit of producing a laser cross-hairtarget on the skin of the patient. This benefit will be discussed ingreater detail below. FIG. 13 illustrates one embodiment of laserreticle 18 comprising a reticle frame 86, radiopaque cross hair marker88, radiolucent front cover 90, radiolucent back plate 91, adjustableclamps 92, sensor tilt LED indicators 94, and an adjustable laseremitter system 96. FIG. 14 illustrates an exploded view of laser reticle18.

Reticle frame 86 may be made of aluminum material in a generallycircular configuration with an inner window opening 98. The purpose ofwindow opening 98 is to allow a fluoroscopic image to pass throughwindow 98 unobstructed by the metal material of frame 86. It should beunderstood that various other suitable materials and configurations maybe used in place of, or in addition to, the reticle frame describedabove. Other reticle frames may include, but are not necessarily limitedto, a generally rectangular configuration with square window opening.With reference to FIGS. 13-14, reticle frame 86 has a front, leadingedge 100 and a back edge 102.

FIG. 15 illustrates, by way of example only, one embodiment ofradiopaque cross hair marker 88. When attached to the receiver 82 of theC-arm 20, radiopaque cross hair 88 is captured in the fluoroscopicimage, giving the operator a reference point to the center of thereceiver 82. Moreover, the cross-hairs 88 provide vertical referenceline in the fluoroscopic image, as discussed below. By way of exampleonly, the radiopaque cross hair marker 88 may be produced from metalBB's 106 fixed onto the radiolucent back plate 91. With reference toFIG. 15, the cross-hair pattern may comprise a single radiopaque BB 106as the exact center, with four lines of BB's extending out from thecenter, along the vertical and horizontal axis of reticle 18. Radiopaquecross hair marker 88 may also comprise a longer, vertical arrow whichpoints to gravity when the reticle is-properly mounted and the C-arm isin the lateral position. Although the radiopaque marker 88 is describedas being formed by metal BB's fixed in a cross-hair pattern onto aradiolucent case, it can be appreciated that other suitable materialsand configurations may be used to produce the same radiopaque targeteffect.

Laser reticle 18 is preferably mounted to the C-arm 82 with the C-arm inthe lateral position, which allows gravity to help correctly positionthe laser reticle 18 and the corresponding radiopaque cross-hair marker88. Laser reticle 18 includes a set of adjustable clamps 92, a sensorpackage (70), and sensor tilt LED indicators 94 to assist in thepositioning of laser reticle 18 on to C-arm 82. As mentioned, a sensorpackage 70, similar to sensor package 22 is integrated within thehousing of the laser reticle 18. The sensor package 70 is preferablysituated such that it is orthogonal to the reference markers 88, andwhen the tilt sensor 70 is perpendicular to the direction of gravity,the sensor registers a zero angle in both the sagittal and transverseplanes. The sensor package is communicatively linked to sensor tilt LEDindicators 94, located near the superior edge of the laser reticle 18,and the center LED indicator will light up when the tilt sensor isperpendicular to the direction of gravity. If the tilt sensor is notperpendicular to the direction of gravity, the sensor tilt LEDindicators 94 will prompt the operator to tilt the laser reticle 18 inthe direction of the lit LED indicator until the center LED indicatorlights up, indicating that the sensor package 70 is perpendicular to thedirection of gravity. Once the laser reticle 18 is leveled out in thisposition, the operator may tighten the adjustable clamps 92 to securelyattach the laser reticle 18 on to the C-arm receiver 82. The use ofadjustable clamps 92 allows laser reticle 18 to attach to nearly anyC-arm. Laser reticle 18 may be shaped in a generally circular pattern tocorrespond to the circular shape of the receiver 82. However, laserreticle 18 may be shaped and dimensioned in any of a number of suitablevariations including, but not necessarily limited to, generallyrectangular, triangular, ellipsoidal, and polygonal.

Laser reticle 18 also includes an adjustable laser cross hair emitter,which may generate a cross-haired target onto the patient's skin at thesurgical access site. Adjustment knobs may be used to adjust the laseremitter along the sagittal and transverse planes. The laser is generatedfrom the center of the laser reticle 18, and when looking down the axisprotruding from the center of the reticle 18 the point of lasergeneration directly overlaps the center point of the radiopaque crosshair 88. An advantage of providing an adjustable laser emitter is toallow the operator to point the laser down any desirable path (and thuscorrect for deformities in the C-arm frame that occur over time). Inparticular, the operator may adjust the laser emitter so that itpropagates directly towards the center of the C-arm signal transmitter80 and down the central axis 85 of the x-ray beam 84. Thus, a perfectvector will be created down the central axis 85 of the x-ray beam85,which may assist the surgeon in determining a preferred starting pointfor skin penetration when performing, by way of example only, a pediclescrew placement procedure, as it will precisely mark with the lasercross hair the skin incision site above and in line with the pedicleaxis when the C-arm 20 is oriented in the owls eye position Whenproperly adjusted, the laser cross-hairs will be aligned with theradiopaque cross-hairs 88. It will be appreciated that the perfectvector benefit may be suitable for use in any number of additionalsurgical actions where the angular orientation or trajectory ofinstrumentation and/or implants is important. It is also appreciatedthat although the laser emitter is described as emitting a cross-hairedpattern, the emitted laser may be shaped in any of a number of suitablevariations including, but not necessarily limited to, a bulls-eye, or asingle point.

FIGS. 16-19 illustrate an adjustable laser emitter system 96 of thelaser reticle 18 that allows the laser emitter to move both up and downand left and right. The laser emitter system comprises a plastic (andradiolucent) light tube 108 extending to the center of the reticle 18from an adjuster assembly 110 coupled to backplate 91. To adjust thelaser emitter 96 up and down, the light tube 108 is coupled to a rockerbar 112 forming part of adjuster assembly 110. A pair of circularapertures (not shown), one in each end of rocker bar 112, pivotallycouple the rocker bar to circular set screws (also not shown) extendinginward from anchors 114. A vertical adjustment knob 116 translates aroller 118 along an incline ramp 120 extending from the rocker bar 112.As the roller 116 engages the incline ramp 120 the rocker bar 112 pivotsaround the set screws coupling the rocker bar to anchors 114 and thelight tube 108 moves along a vertical plane. A tensioned spring 122causes the rocker bar 112 to return to its natural position when theroller 118 is translated back down the ramp 120. A laser emittersituated in rocker bar 112 and coaxial with the light tube 108 directslaser light through the light tube 108. An angled plastic mirror 124 atthe distal end of the light tube 108 redirects the laser light though ahole 126 in the tube. Overlying hole 126 is a defractive optical element128 (DOE). In a preferred embodiment, the DOE 128 is square shaped suchthat the laser light exits the DOE 128 in two perpendicular lines,forming a cross-hairs on the laser target. To adjust the laser emitter96 laterally, the light tube 108 is rotated about its longitudinal axis.To accomplish this, a lateral adjustment knob 130 turns a gear 132coupled to a complementary gear 134 associated with the proximal end ofthe light tube 108. In a preferred embodiment, the laser reticle 18 isequipped with an internal power source to power the laser and the LEDindicators 94. According to one embodiment, the internal power source isa disposable battery 136.

Having described the various components of the surgical trajectorymonitoring system 10, exemplary methods for utilizing the system 10during surgery will now be described. By way of example, the system 10is described herein for use in guided formation of one or more pediclescrew pilot holes for safe and reproducible pedicle screw implantation.It will be appreciated however, that the surgical trajectory monitoringsystem 10 may be used during any of a number of surgical procedureswithout deviating from the scope of this invention. In accordance with afirst general aspect of the present invention, the surgical trajectorymonitoring system may be used to orient and maintain surgical instrument14 along a desired trajectory, for example, during pilot hole formation.The distal end of surgical instrument 14 may first be placed on thepedicle target site in the zero-angle position. The instrument 14 isrotated to the desired reference position, preferably with thelongitudinal axis 26 of sensor clip 12 in line with the longitudinalaxis of the spine. The surgical instrument 14 may then be angulated inthe sagittal plane until the desired cranial-caudal angle is reached.Maintaining the proper cranial-caudal angle, the surgical instrument 14may then be angulated in the transverse plane until the propermedial-lateral angle is attained. Control unit 16 and/or secondaryfeedback system 52 will indicate to the user when the instrument 14 isaligned with the desired angles. Once the angular orientation of theinstrument is correct, the instrument 14 may be advanced into thepedicle to form the pilot hole. The instrument 14 may be rotated backand forth to assist in the formation of the pilot hole. To keep theproper trajectory throughout formation, the instrument 14 mayoccasionally be realigned with the longitudinal axis 26 of the sensorclip 26 in line with the long axis of the spine and the anglemeasurements rechecked. This may be repeated until the pilot hole iscomplete.

To form a pilot hole in a vertebral pedicle with the aid of the surgicaltrajectory system 10, the surgical instrument 14 is advanced to thepedicle target site where the pilot hole is to be formed. This may bedone through any of open, mini-open, or percutaneous access. The precisestarting point for pilot hole formation may be chosen by thepractitioner based upon their individual skill, preferences, andexperience. Methods for determining a starting point with the aid ofsurgical trajectory system 10 are described below.

Upon safely reaching the pedicle target site, the surgical instrument 14is manipulated into the desired angular trajectory. By way of examplethe pedicle axis, defined by a medial-lateral angle A1 (illustrated inFIG. 20) and a cranial-caudal angle A2 (illustrated in FIG. 21), may bedetermined and the pedicle screw and/or related instruments may beadvanced through the pedicle along the desired trajectory. FIGS. 22-23illustrate one exemplary method for manually determining the desiredtrajectory angles, wherein a series of measurements are used todetermine the pedicle axis of the pedicle (or more likely, pedicles)which will receive a pedicle screw. As shown in FIG. 22, preoperativesuperior view MRI or CAT scan images are obtained and used to determinethe medial-lateral angle A1. A vertical reference line is drawn throughthe center of the vertebral body (in the A-P plane). A medial-lateraltrajectory line is then drawn from a central position in the pedicle(e.g. a position within the soft cancellous bone, as opposed to theharder cortical bone forming the outer perimeter of the pedicle) to ananterior point of the vertebral body for the target pedicle. Theresulting angle between the medial-lateral trajectory line and thereference line is measured and the result correlates to themedial-lateral angle A1 of the pedicle axis of the target pedicle, andthus also the medial-lateral angle to be used in forming the pilot hole.The measurement is repeated for each pedicle and the results may benoted and brought to the operating room for reference during thesurgery. Preferably the angles may be input into control unit 16 ofsystem 10 during, as will be described below, for easy retrieval andapplication later.

As shown in FIG. 23, the cranial-caudal angle A2 may be determined usingan intraoperative lateral fluoroscopy image from C-arm 20. A verticalreference line is preferably captured in the lateral fluoroscopy imageto ensure measurements are performed with respect to the direction ofgravity. In a preferred embodiment, this is accomplished through the useof laser reticle 18. The vertical reference line is important as thefluoroscopy image outputs can generally be rotated 360° such that theimage can appear on the monitor in any orientation and a verticalreference line prevents measurements from inadvertently being calculatedfrom an incorrect reference position.

Once the desired trajectory angles are determined for the necessarypedicles, pilot holes may be formed and screws inserted using the tiltsensor 12 to ensure the instruments and implants are aligned with thedetermined angles. As mentioned above, the safety and reproducibility ofpilot hole formation may be further enhanced by employingneurophysiologic monitoring, as will be described in detail below, inconjunction with the trajectory monitoring performed by the surgicaltrajectory system 10.

Without limiting the scope of the present invention, specific exampleswill be described for determining the axis of a vertebral pedicle, or inother words, the angles A1 and A2 described above and for directingpedicle hole formation along the pedicle axis, utilizing variousfeatures of the trajectory monitoring system 10. It will be appreciatedthat various other methods may be utilized to carryout guided pediclescrew pilot hole formation in accordance with the various components ofthe present invention. By way of example only, various features,components, methods and/or techniques that may be used with the surgicaltrajectory monitoring system 10 are shown and described within the PCTPatent App. No. PCT/2007/011962, entitled “Surgical TrajectoryMonitoring System and Related Methods,” filed May 17, 2007, the entirecontents of which are hereby incorporated by reference as if set forthfully herein.

FIGS. 24-25 illustrate, by way of an example only, one embodiment ofscreen display 500 of control unit 16 capable of receiving input from auser in addition to communicating feedback information to the user. Thescreen display 500 incorporates both alpha-numeric and color indicia asdescribed above. In this example (though it is not a necessity) agraphical user interface (GUI) is utilized to enter data directly fromthe screen display. In a surgical procedure of pedicle screw placement,for example, it is advantageous to determine and record themedial-lateral (A1) and cranial-caudal (A2) angle of each pedicle at thedifferent levels of the spinal, i.e. A1 and A2 of L1, A1 and A2 of L2,etc. The GUI of display 500 allows the user to enter the predeterminedA1 and A2 angles of each spinal level and save this information intosurgical system 10. By saving such information, the system 10 mayadvantageously recall the predetermined angles (A1 and A2) for eachspinal level at any given time. It is appreciated that the currentintegrated control system may also be utilized to determine the pedicleaccess angles (A1 and A2). This process is described below. It is alsoappreciated that in addition to its uses in pedicle screw placement, thecurrent embodiment may be suitable for use in any number of additionalsurgical procedures where the angular orientation or trajectory ofinstrumentation and/or implants and/or instrumentation is important,including but not limited to general (non-spine) orthopedics andnon-pedicular based spine procedures

With reference to FIGS. 24-25, measurements obtained for a pre-definedmedial-lateral (M-L) angle A1 may be entered into input boxes 504 and506 for (for left and right pedicles, respectively). Multiple adjustmentbuttons may be used to set the pre-defined angles. FIG. 24 illustrates amethod, by way of example only, of adjusting the left and right M-Langles A1 by using the angle adjustment button sets 503. FIG. 25illustrates another method, by way of example only, of increasing ordecreasing the M-L angles in increments of 10° using the angleadjustment buttons 505 labeled (by way of example only) “+10” and “−10”.More precise angle adjustments may be made by increasing or decreasingthe pre-defined angle in increments of 1° using the angle adjustmentbuttons 507 labeled (byway of example only) “+1” and “−1”. Measurementsobtained for the cranial-caudal (C-C) angle A2 may also be entered intoinput box 510 and adjusted using the angle adjustment button set 511.Level selection menu 508 allows the user to input the predeterminedangle A1 and A2 for each spinal level. The entered values may be savedby the system such that during the procedure selecting the spinal levelfrom level selection menu 508 automatically recalls the inputted values.

Control unit 16 display screen 500 may provide feedback information frommultiple tilt sensors 12 associated with different devices (e.g.instruments 14, C-arm 20, laser reticle 18, etc.). By displayingfeedback information from multiple devices, the information may be usedin conjunction with each other to assist a surgeon in safely performingcomplicated surgical procedures (e.g. pedicle screw implantation, etc.).It is appreciated that further advantages may be gained by combining thetilt sensor data with other relevant data (e.g. neurophysiologicmonitoring data, fluoroscopic images, etc.) to provide an integratedsystem and/or methods for assisting in the performance of the surgicalprocedure. With reference to FIGS. 24-25, display screen 500 provides aC-arm angle window 512 containing-data pertaining to a second tiltsensor 12 positioned on a fluoroscopic imager. By way of example,numeral boxes 514 and 516 display the numeric values of themedial-lateral and the cranial-caudal angles as determined by the C-armtilt sensor 12. Numeric values 514 and 516 may be referenced by the userto help match the M-L and C-C values corresponding to the C-arm sensorwithin an accepted range of the pre-defined target angles A1 and A2 foreach spinal level. If the C-arm is aligned with the pedicle axis (placedin the owls eye view) the C-arm values A1(c) and A2(c), indicated inwindows 514 and 516, should approximate the pedicle axis angles A1 andA2. In another example, the C-arm window 512, or a portion there of(such as the circle 518) may be saturated with the color green when thenumeric values corresponding to the C-arm sensor matches within anaccepted range of the predetermined target angles.

Display screen 500 may also provide feedback information from anothertilt sensor 12 coupled with surgical instrument 14. With reference toFIGS. 24-25, by way of example only, the angular orientation ofinstrument 14 may be communicated to the user in the instrument window522. Instrument window 522 may employ different embodiments to assistthe user in matching the angular orientation of the instrument 14 to thepredefined target angles for each level. With reference to FIG. 24, thecontrol system display 500 employs a color coded target to providefeedback information of the angular orientation of surgical instrument14. The outer rings 524 of the target may be red, the middle rings 526of the target may be yellow, and the inner circle 528 may be green. Whenthe instrument is aligned with the predetermined target angles, thecenter circle may be saturated green, indicating that both themedial-lateral angle A1 and cranial-caudal angle A2 have been matched,or A1=A1(i) and A2=A2(i). If the user wishes to match the angularorientation of the instrument 14 to the angular orientation of theC-arm, the user may make that selection in the “match instrument to”window 509. When instrument 14 is matched to the C-arm (A1(c)=A1(i) andA2(c)=A2(i)) the center circle 528 may be saturated green. The middle526 and outer 524 rings may be divided into quadrants 530, 532, 534, and536 corresponding to right, left, cranial, and caudal, respectively. Byway of example, if the instrument is aligned too far left of the target,the outer 524 or middle 526 ring in the left quadrant 530 will besaturated depending upon how misaligned the instrument is (i.e. whetherit falls into the yellow or red range). Similarly, if the instrument isaligned too far cranially, the outer 524 or middle 526 ring in the upperquadrant 534 will be saturated depending upon how misaligned theinstrument is. If the instrument has matched one of the targeted anglesbut not the other, only the quadrant corresponding to the misalignedangle will be saturated.

In another embodiment of instrument window 522, FIG. 25 employs a colorcoded display, approximating the look of a bubble level, to providefeedback of the angular orientation of the surgical instrument 14. Afree floating ring 538 moves relative to the movement of the instrument.The closer the bubble is to the center, the closer the instrument is tomatching the target angle. When the instrument is within the rangeindicating proper alignment, the ring 538 may be saturated green.Similar to the embodiment of FIG. 30, the user may also have the optionto match the angular orientation of the instrument 14 to the C-armsensor values, rather than the predetermined target values. This optionmay be exercised, by way of example only, by selecting the appropriatebutton in the “match instrument to” window 509. A status bar 520 may beprovided to indicate the relative status of both the instrument 14 andC-arm tilt sensors. By way of example only, the status bar 520 depictedin FIGS. 24 and 25 indicate that both the instrument 14 and the C-armsensors are attempting to match the targeted angles. Other messages (notshown) may indicate for example, that the instrument 12, 80 is trying totarget the C-arm angles, that the target angles are matched, or that asensor is not in use.

FIGS. 26-36 illustrate, by way of example only, another embodiment ofscreen display 600 of an integrated control unit 16. FIGS. 26-36illustrate multiple screen displays of an example embodiment of a“Pedicle Cannulation Assist” (PCA) program designed to integrate datafrom multiple sources. The PCA program may be utilized with anembodiment of the feedback device 16 comprising a computer or similartype processing unit (not shown) capable of receiving input from a useras well as communicating feedback to the user. In similar fashion to thedisplay screen 500, this example utilizes (though it is not necessary) agraphical user interface (GUI) to enter data directly on the screendisplays. The exemplary screen display 600 represents a setup screenfrom which the user may select the desired technique (e.g. “owls eye” or“A/P& Lateral”—described below) to be performed, as well as variousconfigurations utilized within the technique (e.g. integration of livefluoroscopic images, orientation of the C-arm, etc.). Screen display 600includes a header 602 that identifies the program and indicates thecurrent configuration as selected by the user (e.g. Owls eye techniquewith integrated live fluoroscopy as depicted in FIG. 26). Buttons in thetechnique field 604 may be used to select the desired technique to beapplied. By way of example, the “Owl's Eye” button 606 may be touched toselect the Owls Eye technique (described below) and the “A/P & Lateralbutton” may be touched to select the A/P & Lateral technique. In theimaging field 610, buttons 612 and 614 may be touched to select betweenthe options of integrating live fluoroscopic images or proceedingwithout integrated images, respectively. In the orientation field 616,the user may set the orientation of the C-arm (i.e. whether the C-arm ispositioned on the right or left side of the patient) that is to beutilized during the procedure. By way of example, the user may simplytouch the C-arm depiction 618 to toggle from one orientation option tothe next. The start button 620 locks in the selected configuration andadvances the program.

In this embodiment, the feedback device 16 utilizes an image capturesystem (not shown) preferably incorporated within the hardware and/orsoftware in order to retrieve images from the C-arm. When the livefluoroscopic image option is selected display screen 600 may be advanceto a format viewing window to format the image (if necessary), as shownin FIG. 27. The instruction field 620 provides instructions forformatting the image into the appropriate size and/or alignment. Uponselecting the image feed button 622, the fluoroscopic image 630 isretrieved and displayed in the viewing window 624 located in the imagefield 626. As indicated by the instructions in the instruction field620, the image may be resized by, for example only, touching anddragging the bottom right corner of the viewing window 624. The imagemay be aligned by touching (by way of example only) the top left cornerof the viewing window 624 and dragging it until the image is aligned.Button sets 628 and 629 may be provided and utilized as alternative waysto align and resize the image 630, respectively. The proceed button 632locks in the viewing window 624 formatting and advances the program.

A “virtual protractor” display screen is illustrated in FIGS. 28-30. Thevirtual protractor screen may be utilized to input and/or determine theangles to be used during pilot hole formation (i.e. the cranial-caudaland medial-lateral angles discussed elsewhere herein). Data managementfield 634 may be used to view and input angle data in the integratedscreen. The data management field includes an M/L window 636, a C/Cwindow 638, and spinal level buttons 640. Spinal level buttons 640 maybe used to select and indicate the spinal level which corresponds to thedata being input or displayed in the M/L and C/C windows 636 and 638(e.g. level L5 in FIGS. 28 and 29, level L4 in FIG. 30). As previouslydescribed, the medial-lateral angles for each pedicle to be instrumentedare preferably determined preoperatively. The data may be taken to theOR and entered using the M/L window 636. To enter the data, the properspinal level is selected and the edit M/L angles button 644 is selected.As shown in FIG. 29, a keypad 646 appears in the data management field634 and the angles may be entered and saved (or cleared and reentered)for the left and right pedicles. Toggling between the left and rightpedicles may be done by selecting the appropriate buttons labeled, byway of example only, “left” 645 and “right” 647. This may be done inturn for each applicable pedicle. Alternatively, the data may be inputinto the system prior to surgery or entered onto an external memorydevice (e.g. memory cord, USB flash drive, etc.) and transferred to thesystem in the OR in order to reduce the overall surgical time.

The cranial-caudal angles for each pedicle to be instrumented may bedetermined using the virtual protractor 648 superimposed on thefluoroscopic image 630. To accomplish this, the C-arm is oriented in thelateral position such that the image 630 shown on the screen is alateral image. A zero line 650 may be rotated into alignment with thevertical reference line generated in the fluoroscopic image (aspreviously described) by selecting (e.g. touching) and dragging it intoposition. The center point 649 of the virtual protractor 648 may then becentered over the appropriate pedicle by touching the image at thedesired position. The protractor 648 will then position itself, centeredon the position touched. Once positioned over the center of the pedicle,the virtual protractor may be rotated using the control bar 652 until itis aligned with the axis of the pedicle. Selecting the capture C/Cbutton 637 will automatically input and save the angle into theintegrated system as determined by the rotation of the virtualprotractor 648 relative to the zero line 650. With reference to FIG. 37,the user may also enter the C/C angle manually by selecting the editbutton 639 in the C/C window 638. After selecting the edit button 639, aC/C keypad 654 appears and the user may select the appropriate “to foot”or “to head” button to finalize the angle input for the selected level.The C/C angles may be determined and entered for each applicable spinallevel. The proceed button 632 will advance the program into theappropriate technique screen.

By way of example only, FIGS. 31-34 illustrate a main screen display forthe owls eye technique according to one exemplary embodiment. Anindicator 656 shows the relative orientation of the C-arm 20, either APview or lateral view. The indicator 656 does not necessarily correspondto the true AP or true lateral orientations but is rather just a generalindication. For example, as shown here the C-arm is oriented in theowl's eye position which is not a true AP view but is generally closerto a true AP view than a true lateral view. If the C-arm is rotated pasta certain point, by way of example, 60 degrees, the indicator willchange to indicate the opposite view (e.g. lateral). Selecting theoption button 658 expands an option menu 659, illustrated in FIGS.32-33, which may include but is not necessarily limited to, a show orhide angle button 660, a zoom button 662, and a hide button 664. Theshow or hide angle button 660 either opens or closes an instrument anglewindow 668 and C-arm angle window 670 (FIGS. 33 and 34). The zoom button662 zooms in on the fluoroscopic image 630. The hide button 664contracts the options menu 659. A data management field 661 illustratesthe selected spinal level and the cranial-caudal and medial-lateralangels previously input for the selected level. The angles may be editedin the data management field 661 via controls similar to thosepreviously described with reference to virtual protractor screen ofFIGS. 28-30. Instrument and C-arm target indicators, 672 and 678respectively, are positioned opposite each other around the fluoroscopicimage 630. By way of example only, FIG. 34 illustrates the main screendisplay 600 for the owls eye technique when the live fluoroscopy optionis not selected. The display in FIG. 34 is generally the same exceptthat the fluoroscopic image 630 is replaced by a graphic representingthe patient.

The instrument target indicator 672 includes a medial-lateral bar 676and a cranial-caudal bar 674. Individual segments of the targetindicator 672 may be colored to represent the position of the instrumentand relative to the previously determined target angles (displayed inthe data management window 661). The indicator bar 672 may, for example,be shown generally as neutral color (e.g. gray). A single segment oneach of the medial-lateral bar 676 and cranial-caudal bar 674 may behighlighted by a color (e.g. green) to indicate the relative positioninstrument to the target angle. By way of example, the closer thelighted segment is to the target circle, the closer the instrument is tobeing aligned with the corresponding predetermined angle. The size ofthe individual segments may be different and correspond to the range ofvalues encompassed by the segment. By way of example only, the largersegments situated farthest from the target circles correspond to largerranges. In one example, set forth by way of example only, the targetcircle has a range of 3 such that the cranial-caudal target circle willbe highlighted when the instrument is aligned within 3° of thecorresponding cranial-caudal target angle and the medial-lateral targetcircle will be highlighted when the instrument is aligned within 3° ofthe predetermined medial-lateral angle. In one embodiment, the entiremedial-lateral bar 676 is highlighted in the appropriate color (e.g.green) when the instrument is aligned within the range of the targetcircle (e.g. 3 in this example). Similarly, the entire cranial-caudalbar 674 is highlighted in the appropriate color (e.g. green) when theinstrument is aligned within the range of the target circle (e.g. again3° in this example). Thus, when the instrument is aligned within 3° ofthe target medial-lateral angle and 3° of the target cranial-caudalangle, the entire instrument target indicator 672 may be highlighted inthe appropriate color (e.g. green in this example).

In another method, the user may also match the angular orientation ofinstrument 14 to a predefined angular orientation is illustrated usingthe “ball and stick” target indicator 684 of changing length,illustrated in FIG. 33. The length and position of the ball and stickwill indicate to the user the desired orientation of surgical instrument14 in reference to a predefined angular orientation. As illustrated inFIG. 33, one end of the stick is positioned in the center offluoroscopic image 630 and the other end extends outwards from thecenter into the top-left quadrant. This illustration indicates to theuser that the orientation of instrument 14 is not matched up with thepredefined angular orientation. Specifically, indicator stick 684 inFIG. 33 specifies to the user that the angular orientation of instrument14 is too far right in the M-L direction and too far towards the head ofthe patient in the cranial-caudal direction. By way of example only, theuser will adjust instrument 14 in accordance to the position of theindicator stick. As the user adjusts the angular orientation ofinstrument 14 towards the desired angles, the stick indicator willshorten in length. Once the desired angular orientation is found,fluoroscopic image 630 may produce an image of a single dot at thecenter of the image. In another example, the entire fluoroscopic image630, or a portion thereof, may be saturated with the color green angularvalues corresponding to the instrument sensor matches within an acceptedrange of the predetermined target angles. It is appreciated that anysuitable combination of the methods described, whether alone or incombination with another, may be used to indicate to the user theangular orientation of instrument 14 in reference to predefined angles.

Like the instrument target indicator 672, the C-arm target indicator 678includes a medial-lateral bar 680 and a cranial-caudal bar 924.Individual segments of the target indicator 678 may be colored torepresent the orientation of the C-arm relative to the previouslydetermined target angles (displayed in the data management window 661).The C-arm target indicator 678 may, for example, be shown generally asneutral color (e.g. gray). A single segment on each of themedial-lateral bar 680 and cranial-caudal bar 682 may be highlighted bya color (e.g. purple) to indicate the relative position C-arm to thetarget angles. By way of example, the closer the lighted segment is tothe target circle, the closer the C-arm is to being aligned with thecorresponding predetermined angle. The size of the individual segmentsmay be different and correspond to the range of values encompassed bythe segment. By way of example only, the large segments situatedfarthest from the target circles correspond to larger ranges. In oneexample, set forth by way of example only, the target circle has a rangeof 3° such that the cranial-caudal target circle will be highlightedwhen the C-arm is aligned within 3° of the corresponding cranial-caudaltarget angle and the medial-lateral target circle will be highlightedwhen the C-arm is aligned within 3° of the predetermined targetmedial-lateral angle. In one embodiment, the entire medial-lateral bar680 is highlighted in the appropriate color (e.g. purple) when the C-armis aligned within the range of the target circle (e.g. 3 in thisexample). Similarly, the entire cranial-caudal bar 682 is highlighted inthe appropriate color (e.g. purple) when the instrument is alignedwithin the range of the target circle (e.g. again 3° in this example).Thus, when the instrument is aligned within 3° of the targetmedial-lateral angle and 3° of the target cranial-caudal angle, theC-arm target indicator 678 may be highlighted in the appropriate color(e.g. purple in this example).

In use, the C-arm is easily oriented into the owls eye position usingthe C-arm target indicator 678 as a guide. Again, when the owls eyeposition is reached, both the medial-later bar 680 and cranial-caudalbar 682 will fully highlighted in the appropriate color (e.g. purple).Once the C-arm is in the owls eye position, the starting point forinstrument insertion may be determined according to the owls eye methodfor starting point determination previously described above. If the livefluoroscopy option is not chosen, the starting point may be determinedusing the fluoroscopic image monitor 216 as previously described. Whenthe instrument is positioned on the desired starting point, theinstrument may be aligned with the pedicle axis by adjusting theinstrument until both the medial-lateral indicator bar 676 and thecranial-caudal indicator bar 674 of the instrument target indicator arefully highlighted, indicating that the instrument is aligned with thetarget angles which preferably correspond to the pedicle axis. When thetarget indicator 672 shows correct alignment, the instrument may beadvanced into and through the pedicle into the vertebral body. Theprocess may be repeated for each pedicle to be instrumented.

With reference now to FIGS. 41-42, there is shown, by way of exampleonly, main screens display for the A/P & lateral technique option,respectively. The A/P & lateral technique main display is generallysimilar to the owls eye main display above. The A/P & lateral techniquedoes not utilize predetermined target angles and thus the datamanagement field from the owl's eye main display is replaced with a datacapture window 686. Selecting the capture instrument trajectory button688 locks in the medial-lateral and cranial-caudal angles associatedwith the position of the instrument when the button is selected.Thereafter, the instrument target indicator 690 functions as describedabove with the “captured” angles filling the role of the predeterminedtarget angles. Thus, the surgeon is free to determine a desiredtrajectory through any desired means. The instrument target indicator690 will assist the surgeon in maintaining the selected trajectorythereafter. If the C-arm is rotated into the lateral orientation, asdepicted in FIG. 42, the cranial-caudal bar 692 of the instrumentindicator 690 disappears and a protractor 648 is superimposed on thefluoroscopic image 630. The cranial-caudal orientation of the instrumentis thereafter depicted via rotation of the protractor 648.

One example method for using the exemplary A/P & lateral main displayuses predetermined medial-lateral angles as described previously. TheM/L angles are recorded prior to surgery and brought to the OR forreference. The C-arm may be oriented in the lateral view position andthe protractor 648 aligned with the axis of the pedicle. In thisposition the instrument is aligned in the proper cranial-caudalposition. Maintaining the cranial-caudal position, the instrument may beadjusted until the instrument angle window 668 indicates that theinstrument is aligned with the predetermined medial-lateral angle. Oncein this position the capture instrument trajectory button 688 may beselected. Thereafter, the instrument may be advanced into and throughthe pedicle using the instrument target indicator 690 to maintain thetrajectory. This may be repeated for each pedicle to be instrumented.

FIGS. 37-46 illustrate, by way of example only, yet another embodimentof screen display 700 of an display screen system capable of receivinginput from a user in addition to communication feedback from multiplesources (e.g. instrument 15, laser reticle 18, C-arm 20, etc.). Insimilar fashion to the display screen 500 and 600, this example utilizes(though it is not necessary) a graphical user interface (GUI) to enterdata directly on the screen displays. Screen display 700 includes aheader 702 that identifies the program and indicates the currentconfiguration as selected by the user (e.g. Navigated Guidance asillustrated in FIG. 37). Display screen 700 also consists, by way ofexample, test menu bar 704. From menu bar 704, the user may selectand/or change multiple options of the selected configuration. Test menubar 706, by way of example only, may open up a menu bar (not shown),from which multiple neurophysiologic test may be incorporated. In thissetup screen, the user may select a predetermined reference angle (e.g.using pre-defined angles as a reference when implementing the navigatedguidance function of the current system) by pressing reference button708 and selecting a reference option from reference menu 710. The usermay also adjust the image screen of the display by selecting imagingbutton 712.

FIG. 38 illustrates the proceeding screen display from selecting imagingbutton 712. In the imaging field 714, buttons 716 and 718 may be touchedto select between the options of integrating live fluoroscopic imagesfrom the C-arm or proceeding without integrated images, respectively. Inthe imaging controls field, the user may set the orientation of theimage by pressing the flip and rotate button sets, 722 and 724,respectively. The user may also adjust the brightness and contrastingsettings of the image by selecting the appropriate buttons. Displayscreen also consists of an instrument menu bar 730, capable of allowingthe user to make multiple adjustments to multiple integrated feedbackinstruments. From instrument menu bar 730, the user may set theorientation of the C-arm (i.e. whether the C-arm is positioned on theright or left side of the patient) that is to be utilized during theprocedure. The user may select C-arm button 732 labeled, by way ofexample only, “Reticle”. FIG. 39 illustrates the screen display thatfollows the selection of button 732. In the C-arm orientation field 734the user may select the desired C-arm orientation by selecting one ofthe directional buttons 736. C-arm orientation field 734 may alsoinclude an anatomical diagram 738 of a patient to assist the user inselecting the C-arm orientation. Although it is not described, it isappreciated that adjustments may be made for other communicativelylinked instruments that may be selected from instrument menu bar 730.The accept button 740 locks in the selected configuration and advancesthe program. The user may then choose to input the predefined M/L andC/C angles into the system by selecting the level button 742 on menu bar704.

FIG. 40 illustrates, by way of example only, the advancing screen fromthe selection of level button 742. FIG. 40 also illustrates the user'soption of hiding the instrument menu bar 730 by pressing menu hidebutton 741. From this screen the user may input the M/L angles (A1) andC/C angle (A2) for each pedicle level in the data management field 744.Data management field 744 may be used to view and input angle data inthe integrated screen. The data management field includes an M/L window746, a C/C window 748, and spinal level buttons 750. Spinal levelbuttons 750 may be used to select and indicate the spinal level whichcorresponds to the data being input or displayed in the M/L and C/Cwindows 746 and 748. As previously described, the medial-lateral anglesfor each pedicle to be instrumented are preferably determinedpreoperatively. The data may be taken to the OR and entered using theM/L window 746. From the M/L window 746, the user may input thepredefined M/L angles by increasing or decreasing the right or left M-Langles in increments of 10° using the angle adjustment buttons 752labeled (by way of example only) “+10” and “−10”. More precise angleadjustments may be made by increasing or decreasing the pre-definedangle in increments of 1° using the angle adjustment buttons 754 labeled(by way of example only) “+1” and “−1”. Measurements obtained for thepre-defined cranial-caudal (C-C) angle A2 may also be entered into C/Cwindow 748. By way of example only, pre-defined C/C angle A2 may beentered though either the virtual protractor function (described in moredetail below) or angle A2 may be entered manually. The user may selecteither of these functions by pressing the “Virtual Protractor” button756 and the “Edit Manually” button 758, respectively.

FIGS. 41-42 illustrate, by way of example only, the subsequent virtualprotractor onscreen display of the system when the user selects the“Virtual Protractor” button 756. In this screen, the user is givenanother opportunity to make additional adjustments to the image of thefluoroscopic image from the imaging controls field 760. It is appreciatethat throughout the program, the user may make many adjustments to thesystem (e.g. adjust the fluoroscopic image, change the reference angles,make adjustments to instrument controls, etc.). The chief purpose ofthis integrated screen display is to determine the angles to be usedduring a surgical procedure, such as pilot hole formation (i.e. thecranial-caudal and medial-lateral angles discussed elsewhere herein).Spinal level buttons 750 may be selected to input the C/C angle for eachlevel. The C/C angles for each pedicle to be instrumented may bedetermined using the virtual protractor 762 superimposed on thefluoroscopic image 770. To accomplish this, the C-arm is oriented in thelateral position such that the image 770 shown on the screen is alateral image. A zero line 764 may be rotated into alignment with thevertical reference line generated in the fluoroscopic image (aspreviously described) by selecting (e.g. touching) and dragging it intoposition. The center point 766 of the virtual protractor 762 may then becentered over the appropriate pedicle by touching the image at thedesired position. The protractor 762 will then position itself, centeredon the position touched. Once positioned over the center of the pedicle,the virtual protractor may be rotated using the control button 768 untilit is aligned with the axis of the pedicle. Selecting the save imagebutton 772 will input the angle determined by the rotation of thevirtual protractor 762 relative to the zero line 764. With reference toFIG. 42, the user may choose to give the image a file name in save field774. Virtual protractor screen may also consist of head and footdiagrams 776 to assist the user in understanding the orientation of thepatient. The determined C/C angle may be displayed in C/C angle displaywindow 778. Return button 780 brings the user back to the screen displayillustrated in FIG. 40.

FIG. 43 illustrates, by way of example only, the subsequent onscreendisplay of the system when the user selects the “Edit Manually” button758 of FIG. 40. In this example, similar to the process of adjusting thepre-defined M-L angles A1 above, the pre-defined C-C angle A2 may beincreased or decreased in increments of 10° and 1° by pressing the angleadjustment buttons, 782 and 784, accordingly. Furthermore, the directionof the pre-defined C-C angle A2 may be entered by pressing the cephalad(towards the head) button 786 and caudal (towards the feet) 788. Theuser may also manually input the C/C angle at each spinal level byselecting one of the appropriate spinal level buttons 750. By pressingthe save button 772, the entered values may be saved by the system suchthat during the procedure selecting the spinal level from “Reference”menu 517 automatically recalls the inputted values.

FIGS. 44-46 illustrate, by way of example only, onscreen displays of thesystem with feedback information from multiple sources. Viewing window790 may capture a fluoroscopic image from the C-arm, as illustrated inFIG. 44, to assist the operator in determining the fixed angles of thepedicle in pedicle placement procedures. However, the user may choosenot to display a fluoroscopic image, and instead utilize a graphic inits replacement, as illustrated in FIGS. 45-46. Viewing window 790utilizes a cross-hair reference 792 (not visible in FIG. 44) to indicatethe center of the image from the C-arm. Center reference 792 may assistthe user in procedures which require the surgeon to operate along adesired angular trajectory to the spine. Display 700, in thisembodiment, also consists of other feedback information windows toassist the surgeon during operation. Instrument window 794 providesfeedback information to the user of the angular orientation of theattach instrument 14. When the angular orientation of the instrument isin accordance with the predefined angular orientation, the system mayalert the user of the match. By way of example only, instrument window794 may be saturated with a color (e.g. green) to indicate the properalignment of the instrument. Instrument window 794 may also providealphanumeric feedback. When the angular orientation of the instrument isproperly aligned with the predefined angles, the M/L angles and the C/Cangles with match accordingly (A1(i)=A1). Menu bar 704 may also providethe predefined reference angles for each level to compare with thefeedback information of the various instruments. C-arm window 796 mayalso communicate feedback information to the user. In similar fashion toinstrument window 794, feedback information from the angular orientationof the C-arm may be utilized. FIGS. 44 and 45 illustrate an additionalC-arm window 798 depicted the orientation of the C-arm as in relation tothe patient.

FIG. 46 illustrates, by way of example only, the onscreen display 700 ofa display screen system when running neurophysiologic test.Neurophysiologic button 797 allows the user to run neurophysiologictest. By way of example only, the user may select to run a dynamicstimulated EMG test while continuing to run the navigated guidancefeatures of the current system with feedback information from multiplesources. Stop button 799 allows the user to stop stimulation whenrunning a test. FIG. 46 also illustrates the integrated system's abilityto recall saved recordings from the history menu 795

The surgical trajectory system 10 described above may be used incombination with any number of neurophysiologic monitoring systems.These may include, but are not necessarily limited to, neurophysiologicmonitoring systems capable of conducting pedicle integrity assessmentsbefore, during, and after pilot hole formation, as well as to detect theproximity of nerves while advancing and withdrawing the surgicalinstrument 14 from the pedicle target site. By way of example, thesurgical trajectory monitoring system 10 may be used in conjunction withthe neuromonitoring system 400, illustrated by way of example only inFIG. 47. A neuromonitoring system is shown and described in the commonlyowned and co-pending U.S. patent application Ser. No. 12/080,630,entitled “Neurophysiology Monitoring System,” and filed on Apr. 3, 2008the entire contents of which is hereby incorporated by reference as ifset forth fully herein. Neuromonitoring system 400 may perform, by wayof example, the Twitch Test, Free-run EMG, Basic Screw Test, DifferenceScrew Test, Dynamic Screw Test, MaXcess® Detection, and Nerve Retractor,all of which will be described briefly below. Functionality ofneuromonitoring system 400 has been described in detail elsewhere andwill be described only briefly herein. The Twitch Test mode is designedto assess the neuromuscular pathway via the so-called “train-of-four”test to ensure the neuromuscular pathway is free from muscle relaxantsprior to performing neurophysiology-based testing, such as boneintegrity (e.g. pedicle) testing, nerve detection, and nerve retraction.This is described in greater detail within PCT Patent Application No.PCT/US2005/036089, entitled “System and Methods for Assessing theNeuromuscular Pathway Prior to Nerve Testing,” filed Oct. 7, 2005, theentire contents of which is hereby incorporated by reference as if setforth fully herein. The Basic Screw Test, Difference Screw Test, andDynamic Screw Test modes are designed to assess the integrity of bone(e.g. pedicle) during all aspects of pilot hole formation (e.g., via anawl), pilot hole preparation (e.g. via a tap), and screw introduction(during and after). These modes are described in greater detail in PCTPatent Application No. PCT/US2002/035047 entitled “System and Methodsfor Performing Percutaneous Pedicle Integrity Assessments,” filed onOct. 30, 2002, and PCT Patent Application No. PCT/US2004/025550,entitled “System and Methods for Performing Dynamic Pedicle IntegrityAssessments,” filed on Aug. 5, 2004 the entire contents of which areboth hereby incorporated by reference as if set forth fully herein. TheMaXcess® Detection mode is designed to detect the presence of nervesduring the use of the various surgical access instruments of theneuromonitoring system 400, including the k-wire 427, dilator 430,cannula 431, retractor assembly 432. This mode is described in greaterdetail within PCT Patent Application No. PCT/US2002/022247, entitled“System and Methods for Determining Nerve Proximity, Direction, andPathology During Surgery,” filed on Jul. 11, 2002, the entire contentsof which is hereby incorporated by reference as if set forth fullyherein. The Nerve Retractor mode is designed to assess the health orpathology of a nerve before, during, and after retraction of the nerveduring a surgical procedure. This mode is described in greater detailwithin PCT Patent Application No. PCT/JS2002/030617, entitled “Systemand Methods for Performing Surgical Procedures and Assessments,” filedon Sep. 25, 2002, the entire contents of which are hereby incorporatedby reference as if set forth fully herein. The MEP Auto and MEP Manualmodes are designed to test the motor pathway to detect potential damageto the spinal cord by stimulating the motor cortex in the brain andrecording the resulting EMG response of various muscles in the upper andlower extremities. The SSEP function is designed to test the sensorypathway to detect potential damage to the spinal cord by stimulatingperipheral nerves inferior to the target spinal level and recording theaction potential from sensors superior to the spinal level. The MEPAuto, MEP manual, and SSEP modes are described in greater detail withinPCT Patent Application No. PCT/JS2006/003966, entitled “System andMethods for Performing Neurophysiologic Assessments During SpineSurgery,” filed on Feb. 2, 2006, the entire contents of which is herebyincorporated by reference as if set forth fully herein.

With reference to FIG. 47, the neurophysiology system 400 includes adisplay 401, a control unit 402, a patient module 404, an EMG harness406, including eight pairs of EMG electrodes 408 and a return electrode410 coupled to the patient module 404, and a host of surgicalaccessories 412, including an electric coupling device 414 capable ofbeing coupled to the patient module 404 via one or more accessory cables416. To perform the neurophysiologic monitoring, the surgical instrument14 is configured to transmit a stimulation signal from theneurophysiology system 400 to the target body tissue (e.g. the pedicle).As previously mentioned, the probe members 30 may be formed of materialcapable of conducting the electric signal. To prevent shunting of thestimulation signal, the probe member 30 may be insulated.

The neurophysiology system 400 performs nerve monitoring during surgeryby measuring the degree of communication between a stimulation signaland nerves or nerve roots situated near the stimulation site. To dothis, the surgical instrument is connected to the neurophysiologymonitoring system 400 and stimulation signals are activated and emittedfrom the distal end. EMG electrodes 408 positioned over the appropriatemuscles measure EMG responses corresponding to the stimulation signals.The relationship between the EMG responses and the stimulation signalsare then analyzed by the system 400 and the results are conveyed to thepractitioner on the display 401. More specifically, the system 400determines a threshold current level at which an evoked muscle responseis generated (i.e. the lowest stimulation current that elicits apredetermined muscle response). Generally the closer the electrode is toa nerve the lower the stimulation threshold will be. Thus, as the probemember or surgical access members move closer to a nerve, thestimulation threshold will decrease, which may be communicated to thepractitioner to alert him or her to the presence of a nerve. The pedicleintegrity test, meanwhile, works on the underlying theory that given theinsulating character of bone, a higher stimulation current is requiredto evoke an EMG response when the stimulation signal is applied to anintact pedicle, as opposed to a breached pedicle. Thus, if EMG responsesare evoked by stimulation currents lower than a predetermined safelevel, the surgeon may be alerted to a possible breach. The surgicalinstrument 14 may be connected to the neurophysiology system 400 bythrough sensor clip 12. By way of example and with reference to FIG.2-3, an additional cable 47 may couple the clip 12 to theneurophysiology system 400. Attached to the cable 47, inside the endhook48, is an exposed wire 49 that contact the exposed proximal portion 40of instrument 14.

During pilot hole formation, while the trajectory of the surgicalinstrument is being monitored to prevent the instrument from breachingthe pedicle walls, pedicle integrity assessments may be performed toalert the practitioner in the event a breach does occur. Stimulationsignals are emitted from the electrode, which should be at leastpartially positioned within the pedicle bone during hole formation. Thestimulation threshold is determined and displayed to the surgeon via theneurophysiology monitoring system 400. Due to the insulatingcharacteristics of bone, in the absence of a breach in the pedicle wall,the stimulation threshold current level should remain higher than apredetermined safe level. In the event the threshold level falls belowthe safe level, the surgeon is alerted to the potential breach. When thepilot hole is fully formed, a final integrity test should be completed.

In one embodiment, the neurophysiology system 400 control unit and thesurgical trajectory system 10 control unit 16 may be integrated into asingle unit. Neurophysiology monitoring and trajectory monitoring may becarried out concurrently and the control unit may display results foreach of the trajectory monitoring function and any of the variety ofneurophysiology monitoring functions. Alternatively, the control unit 16and control unit 402 may comprise separate systems and the sensor clip12 may be communicatively linked directly to control unit 402 of theneurophysiology monitoring system and the control unit 16.

While the invention is susceptible to various modifications andalternative forms, (such as the drill bit, needle points, and T-handlementioned above) specific embodiments thereof have been shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the description herein of specific embodimentsis not intended to limit the invention to the particular formsdisclosed, but on the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the scopeand spirit of the invention as defined herein. By way of example, themethod for determining the cranial-caudal A2 has been described hereinas taking place intraoperatively using lateral fluoroscopy imaging.However, the cranial-caudal angle may also be determined preoperativelyemploying various imaging and/or computer processing applications. Forexample, a 3-D model of a patient's vertebra (or other applicable bodypart) may be obtained using a combination of medical imaging andcomputer processing. From the 3-D model the angle A2 may be calculatedafter which the determined value may be utilized by the surgicaltrajectory system and methods described above. It is furthercontemplated that computer processing of medical images may be used toextrapolate the pedicle axis angles A1 and A2 without the need for humanintervention. Finally, it will be appreciated that the intraoperativemonitoring discussed herein has generally focused on the use of a C-armfluoroscopic imager, however, orienting the C-arm with a tilt sensor andproviding a trajectory oriented reticle/plumb line using the methods andsystems described herein may apply to any form of intraoperativemonitoring.

What is claimed is:
 1. A method comprising: receiving, at a computer, gravitational angular orientation data during a spine surgery from a tilt sensor coupled to an instrument; determining, with the computer and based on the gravitational angular orientation data, a first angular orientation between two locations of anatomical structures within a first fluoroscopic image based on a vertical reference line relative to gravity and a medial-lateral trajectory line from a central position in a pedicle to an anterior point of a vertebral body; determining, with the computer and based on the gravitational angular orientation data, a second angular orientation between two locations of anatomical structures within a second fluoroscopic image; displaying, at a display communicatively linked to the computer, a first indicia of the first angular orientation between two locations within the first fluoroscopic image; displaying, at the display, a second indicia of the second angular orientation between two locations within the second fluoroscopic image; displaying, at the display, a third indicia of a variance between the first angular orientation and a first predetermined target angle; displaying, at the display, a fourth indicia of a variance between the second angular orientation and a second predetermined target angle; and displaying, at the display, the first fluoroscopic image or the second fluoroscopic image.
 2. The method of claim 1, wherein the third indicia includes at least one of: a first color indicative of an optimal variance between the first angular orientation and the first predetermined target angle; a second color indicative of an unacceptable variance between the first angular orientation and the first predetermined target angle, and a third color indicative of an acceptable yet not optimal variance between the first angular orientation and the first predetermined target angle.
 3. The method of claim 1, further comprising: providing one or more instructions for overlaying a virtual protractor on the display.
 4. The method of claim 3, further comprising: determining an angular orientation between a plurality of locations according to a plurality of points associated with the virtual protractor on the display.
 5. The method of claim 4, further comprising: receiving one or more inputs adjusting at least one of the plurality of points associated with the virtual protractor.
 6. The method of claim 1, wherein the second angular orientation between the two locations within the second fluoroscopic image is based on a vertical reference line relative to gravity and the medial-lateral trajectory line.
 7. The method of claim 1, further comprising: monitoring neurophysiologic changes.
 8. The method of claim 1, further comprising: receiving one or more inputs for adjusting at least one of the first predetermined target angle and the second predetermined target angle intraoperatively.
 9. A method comprising: receiving gravitational angular orientation data during a spinal surgery from a tilt sensor coupled to an instrument; determining a first angular orientation between two anatomical structures within a first fluoroscopic image based on: an angle between a vertical reference line relative to gravity and a medial-lateral trajectory line from a central position in a pedicle to an anterior point of a vertebral body; or an angle between virtual reference line relative to graving and a cranial-caudal trajectory line of a spine from a central position in the pedicle to an anterior point of the vertebral body; determining a second angular orientation between two anatomical structures within a second fluoroscopic image based on the gravitational angular orientation data; displaying a first indicia of the first angular orientation; displaying a second indicia of the second angular orientation; displaying a third indicia of a variance between the first angular orientation and a predetermined target angle; and displaying a fourth indicia of a variance between the second angular orientation and a second predetermined target angle.
 10. The method of claim 9, wherein the third indicia is: a first color indicative of an optimal variance between the first angular orientation and the predetermined target angle; a second color indicative of an unacceptable variance between the first angular orientation and the predetermined target angle; or a third color indicative of an acceptable yet not optimal variance between the first angular orientation and the predetermined target angle.
 11. The method of claim 9, further comprising: overlaying a virtual protractor on the display; determining an angular orientation between a plurality of locations within a fluoroscopic image according to a plurality of points associated with the virtual protractor; and receiving one or more inputs for adjusting at least one of the plurality of points associated with the virtual protractor.
 12. A method comprising: receiving gravitational angular orientation data from a tilt sensor coupled to an instrument; determining a first angular orientation between two anatomical structures within a first fluoroscopic image based on a line from a central position in a pedicle to an anterior point of a vertebral body relative to gravity; and determining a second angular orientation between two anatomical structures within a second fluoroscopic image; determining a first variance between the first angular orientation and a first predetermined target angle; determining a second variance between the second angular orientation and a second predetermined target angle; displaying a first indicia of the first variance; and displaying a second indicia of the second variance.
 13. The method of claim 12, further comprising: selecting a first color responsive to the first variance being an optimal variance between the first angular orientation and the predetermined target angle; selecting a second color responsive to the first variance being an unacceptable variance between the first angular orientation and the predetermined target angle; and selecting a third color responsive to the first variance being an acceptable yet not optimal variance between the first angular orientation and the predetermined target angle.
 14. The method of claim 12, further comprising: providing a virtual protractor; determining an angular orientation between a plurality of locations according to a plurality of points associated with the virtual protractor on the display; and adjusting at least one of the plurality of points associated with the virtual protractor.
 15. The method of claim 12, further comprising: monitoring neurophysiologic changes.
 16. The method of claim 12, further comprising: receiving one or more inputs for adjusting at least one of the predetermined angle and the second predetermined angle intraoperatively.
 17. The method of claim 12, further comprising: obtaining additional angular orientation data from a sensor coupled to an intraoperative imaging device; and providing an indicia of the additional angular orientation data.
 18. The method of claim 12, further comprising: activating one or more lights coupled to the instrument based on a direction the instrument must travel to align with a vertebral pedicle based on the first or second angular orientation.
 19. The method of claim 12, further comprising: advancing a distal end of the instrument into a vertebral pedicle.
 20. The method of claim 12, further comprising: providing feedback of angular orientation of the instrument with a floating graphic moving relative to a center of a fixed graphic. 